Geological and Geospatial Mapping of Vulnerability Areas for Proper Flood Mitigation: Ganaja, Lokoja Metropolis, North-Central Nigeria

Abstract

This study aimed at the geological and geospatial mapping of flood vulnerable areas in Ganaja, Lokoja metropolis for proper flood mitigation. The geological mapping of the study area involved taking several traverses and understudying the different rock types in the study area. Rocks identified are porphyritic granite, migmatite, augen gneiss, aplitic granite, medium-grained granite, pegmatitic intrusions and quartzo-feldspathic veins, banded gneiss and biotite gneiss. Fractures and joint within the rocks show NW-SE, NNE-SSW orientations; corresponding to the predominant stress direction that represent imprints of the Pan-African orogeny. The incessant inundation of the settlement by floods has necessitated this risk and vulnerability assessment. Results from the geospatial investigation identified three areas with respect to vulnerability level. Buildings within 100 meters buffer distance from the river banks and flood plains are highly vulnerable, those within 200 meters buffer distance is moderately vulnerable while those 300 meters above buffer distance are less vulnerable areas. The relationship between the geology or geomorphology of the area and its effect on flood vulnerability is clearly seen from the geologic, elevation and vulnerability maps of the study area. The contour intervals in the western section is seen to have steeper slopes thereby allowing for easy run-off while the eastern section, having the flood plains of River Niger; have more gentle slopes with a tendency to accumulate water.